The present invention relates to an inverter connection having terminals for connection to a d.c. voltage source, with at least one inverter bridge, in which each valve branch consists of a thyristor and a diode connected in anti-parallel therewith, which thyristor and diode may be combined in a single component, the inverter bridge being connected between the terminals in series with a valve consisting of a second thyristor and a second diode connected in anti-parallel therewith, which second thyristor and second diode may also be combined in a single component, the inverter bridge being further connected to a turn-off circuit for turning off all the thyristors, which turn-off circuit comprises a capacitor connection and a turn-off thyristor means.
In an inverter bridge it is previously known to arrange a common turn-off circuit for turning off all the valves of the bridge simultaneously. For example, FIG. 9 in British Patent Specification No. 1,264,538 shows an example of an inverter connection of this previously known kind. This known connection, however, has considerable disadvantages.
For one thing, the prior art connection shows two thyristors (11, 8) which are connected in series with each other directly to the d.c. voltage source. If, through a malfunction, these two thyristors should become conducting at the same time, the d.c. voltage source would become short-circuited through the thyristors. This short-circuit path has no impedance elements whatsoever to limit the short-circuit current, and therefore there is a considerable risk that the thyristors will become destroyed in the case of a malfunction of the kind stated.
Secondly, in the prior art connection, the point of connection between the commutation thyristors 8 and 11 is at a potential which exceeds the supply voltage. The potential of the said point is dependent on the figure of merit of the turn-off circuit and on the "ignition" times of the thyristors, and is therefore insufficiently controlled and may assume high values. The thyristors 8 and 11 must therefore be dimensioned for high voltages, which involves an economical and practical disadvantage.